1. Field of the Invention
The present invention relates to a software defined radio device having a function modifiable by a software modification, and a method for renewing software for downloading software and renewing a function of a software defined radio device, and a software defined radio system for providing software to a software defined radio device.
2. Description of the Related Art
A software defined radio device (SDR: Software Defined Radio) includes a signal processor such as a FPGA (Field Programmable Gate Array) and a DSP (Digital Signal Processor) and is configured to realize wireless communication function corresponding to various communication methods by changing the installed software. Software defined radio devices require preventive measures due to the risk of improper use such as transmissions of unlawful radio waves, disturbances such as radio wave interference, and malfunction of the device, etc. in the case where improper software or altered software not authorized by the device or its owner is installed.
Therefore, it is necessary to enable a download of unaltered software only by a software defined radio device authorized by the software provider. Furthermore, it is necessary to maintain the confidentiality of the content of the software from third parties. In other words, it is necessary to provide security (confirmation via a communication channel of being unaltered), validity (confirmation of a communication entity as being valid), and confidentiality (being unreadable even when intercepted).
Technology for correctly downloading software by a software defined radio device disclosed hitherto includes, for example, “Software Defined Wireless Device and Method for Controlling the Same” (see: Japanese Published Unexamined Patent Application No. 2004-213339) and “Wireless Communication Device, and Method for Program Downloading, and Computer Program” (see: Japanese Published Unexamined Patent Application No. 2003-304235).
Regarding the guarantee of the validity of the software by these technologies, a distributor distributes an electronic signature attached to the software by public key encryption; the software defined radio device at a receiving end verifies the electronic signature; and thereby the validity of the software is confirmed. Furthermore, Japanese Published Unexamined Patent Application No. 2003-304235 discusses technology for switching among the use of hash functions, keys, encryption methods, and the like to improve the validity and concealability of the software.
As an example of technology for maintaining the confidentiality of a communication, Japanese Published Unexamined Patent Application No. 2005-269128 discusses technology for selecting one common key for each communication from a plurality of common keys, communicating only an index thereof, encrypting the data transmission, and decrypting the data transmission. Furthermore, the technology discussed in Japanese Published Unexamined Patent Application No. 2005-269128 confirms the data as being unaltered by using a hash value.
Additionally, in the case where encrypted communication is performed between devices, hitherto technology includes a relay device for decrypting encrypted data and then transmitting after encrypting with a separate common key (see: Japanese Published Unexamined Patent Application No. H10-341223). Furthermore, this Patent Reference discusses the use of a combination of a public key and a private key in one of the communication intervals.
However, the communication method of the software defined radio device is changed, and therefore during the software download, it is preferable for the software defined radio device to perform the verification of the validity using a small calculation amount and in a short period of time.
The technologies discussed in the patent references recited above verify the validity using an electronic signature of a public key encryption, but generally, the processing required by a public key encryption is more than that of a common key encryption. For the constrained processing capacity of portable wireless devices, embedded devices, and the like, a tradeoff unfortunately occurs between the processing time and the security of the download.
Furthermore, in light of the limited memory capacity of software defined radio devices, the software data of all of the corresponding communication methods cannot be stored in the software defined radio device. In such a case, it is necessary to frequently interchange the software data. Therefore, a configuration providing a high speed verification of the validity of downloaded software is required. However, simply replacing a public key encryption with a common key encryption is unfortunately insufficient for protecting the security once the common key is compromised.
In light the problems recited above, the present invention is directed to provide: a software defined radio device for maintaining the security of software downloads while reducing the amount of processing necessary for verifying the validity of the downloaded software and performing the verification at high speed; a method for renewing software of the software defined radio device; and a software defined radio system.